I'd like to upgrade our servers from 5.1 to 5.5 and seeking feedback on reliability/stability of doing so. I'd like to do the upgrade if I'm confident that 5.5 support is relatively stable and reliable at this point and if probability of introducing any new issues is extremely low.

Over the past months, I've seen various cpanel releases mentioning 5.5-related fixes, but haven't noticed those lately so I suppose that must be a good sign.

Staff Member

The biggest issue I've seen cropping up with MySQL 5.5 is the open files limit being reached far more easily. I'd highly suggest if you are considering updating to use the following forum thread to increase the open files limit on the system for MySQL and within MySQL itself:

Thanks Tristan. Is it understood why the open files limits are being reached when moving to 5.5? Perhaps this relates to the way it uses multiple cores more efficiently and thus is processing more threads in parallel? Or perhaps it is simply that some users who migrate are not re-optimizing mysql after migrating ... ?

Staff Member

It doesn't have to do with MySQL Optimization so far as I've been able to determine. It has to do with a system limit being placed on MySQL that the newer MySQL 5.5 appears to reach far easier than prior versions. I don't know if this is due to speed improvements and MySQL opening more files or not. I do know that we've seen a large number of tickets on it.